Due to a rapid increase in the use of fossil fuels, there is an increasing demand for the use of alternative energy or clean energy, and thus research into power generation and energy accumulation fields is being most actively conducted.
As a representative example of electrochemical devices using such electrochemical energy, secondary batteries are currently used and use thereof tends to gradually expand. Recently, in line with an increase in development of technology for portable devices, such as portable computers, mobile phones, cameras, and the like, and demand therefor, demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, much research into lithium secondary batteries, which have high energy density, high operating voltage, long cycle lifespan, and a low self-discharge rate, has been conducted, and such lithium secondary batteries are commercially available and widely used.
Generally, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. In the secondary battery, energy transfer occurs while lithium ions reciprocate between opposite electrodes such that, through I′ charging, lithium ions from a positive electrode active material are intercalated into a negative electrode active material such as carbon particles and, during discharging, the lithium ions are deintercalated, and, in this way, the secondary battery can be charged and discharged.
For example, a lithium secondary battery has a structure in which an electrode assembly, including a positive electrode including a lithium transition metal oxide as an electrode active material, a negative electrode including a carbon-based active material, and a porous separator, is impregnated with a lithium electrolyte. The positive electrode is manufactured by coating aluminum (Al) foil with a positive electrode mixture including a lithium transition metal oxide, and the negative electrode is manufactured by coating copper (Cu) foil with a negative electrode mixture including a carbon-based active material.
Meanwhile, to achieve high capacity of the secondary battery, while performance such as lifespan, resistance, and the like is maintained at the same level, it is necessary to realize a high-density electrode to utilize a negative electrode active material as much as possible within unit volume.
Conventionally, there have been attempts to realize a high-density electrode by pressing a negative active material to the maximum extent without considering physical properties thereof, which results in peeling, cracks, or the like of the active material, thus causing a resistance increase and deterioration of lifespan characteristics.
Therefore, there is a need to develop a method of improving battery performance via realization of electrode density that enables optimum performance according to the type of negative electrode active material.